Module 3: Structure and Function of the Plasma Membran

membrane

the outer border of all cells and organelles, it helps

• manage what enters and exits the cell

• helps receive external signals

• help initiate cellular responses

• helps cells bind and attach to surfaces and other cells

fluid mosaic model

fluid: there is a fluid filling in the cells and it is dynamic

mosaic: the membrane is made up of many molecules like lipids, phospholipids, cholesterol, proteins, and carbs

the components of the membrane can change based on the environment of the membrane

phospholipids in a cell membrane

amphipathic lipid molecules that compose the bulk of the membrane

• The hydrophillic head is made of a glycerol molecule and a phosphate group (polar)

• The hydrophobic tail is made of 2 fatty acid chains

phospholipid bilayer

hydrophobic fatty acids face each other in the interior, hydrophillic phosphate groups face the aqueous environment outside the cell

glycoprotein

protein with carb attached

glycolipid

lipid with carb attached

peripheral membrane proteins

attached to only the surface of the membrane

anchored membrane protein

attached to the membrane because of an associate with another protein or lipid

integral membrane protein

built into the membrane

transmembrane proteins

span the entire membrane

integral proteins structure

they need to have one or more regions that are hydrophobic (ade of hydrophobic amino acids) and others that are hydrophillic

shape of the bilayer

they are asymmetric

interior proteins

anchor fiber of the cytoskeleton to the membrane

exterior proteins

bind to the extracellular matrix

glycoproteins

they bind to substances the cell needs to import

3rd major component of membranes

Carbs, they are always located on the outside part of the cell membrane

• protein: glycoprotein

• lipid: glycolipid

and has a function in cell to cell recognition

CD4 receptors

glycoproteins that are compatible with proteins on the surface of HIV, HIV has surface proteins and carbs disguise it as self

how the length of fatty acids affect membrane fluidity

• If shorter=more fluidity

• If longer=more rigid

This is because the longer the fatty acids are the more likely they are to tangle, making the phospholipids unable to move

How the saturation of fatty acid tails affect membrane fluidity

• unsaturated=more fluid

• saturated=more rigid

This is because unsaturated fatty acids are bent and therefore don’t pack as tightly

how temperature affects membrane fluidity

• higher temp=more fluid

• lower temp=more rigid

This is because molecular movement speeds up at high temperatures, but it can’t be to warm or the membrane will fall apart

how do membranes adjust themselves regarding fatty acids

if it is to warm cells will add phospholipids with longer and saturated fatty acids to maintain the rigid nature. If it is to cold cells will add phospholipids with shorter and unsaturated fatty acids to increase fluidity

how do membranes adjust themselves regarding cholesterol

In hot temperatures it helps the membrane be less fluid by filling in the gaps between fatty acids, when it is cold the cholesterol helps the fatty acids not pack to tightly

the plasma membrane is selectively permeable

not all substances can cross, small nonpolar molecules (gasses) can pass directly through the membrane

can small uncharged polar molecules pass through the membrane?

they can but not as easily as nonpolar molecules because they will have a tough time getting over the hydrophobic region of the membrane

can large polar molecules pass through the membrane?

they do not travel through membranes because of their size

can small ions pass through the membrane?

no, because they carry full charges that cannot pass through the center of the bilayer

passive transport

molecules move in response to a concentration gradient from an area of high concentration to area of low concentration

active transport

requires ATP to go against a concentration gradient

bulk transport

a type of active transport that allows movement of very large or abundant things across a membrane

simple diffusion

the movement of high concentration to low concentration, until the concentration is equal across a space/membrane (equilibrium)

what molecules go through simple diffusion

small nonpolar molecules (lipid hormones, O2, CO2)

why does simple diffusion happen

this happens because when there are a lot of molecules they are more likely to bump into eachother making them want to go in the free space

diffusion rate

how quickly a molecule will go through diffusion

how the concentration gradient affects diffusion rate

greater difference faster diffusion

how the mass of the molecules affects diffusion rate

smaller molecules diffuse quicker

how the temperature affects diffusion rate

molecules move faster when temperatures are higher

how the solvent density affects diffusion rate

dehydration increases density of cytoplasm = reduced diffusion rates

how the solubility affects diffusion rate

more nonpolar (lipid soluable) materials diffuse faster

how the surface area affects diffusion rate

increased surface area speeds up diffusion rates

how the distance travelled affects diffusion rate

the greater the distance, the slower the rates; important factor affecting upper limit of cell size

how the pressure affects diffusion rate

higher pressure = faster diffusion rates

what molecules go through facilitated diffusion

polar molecules/ions

integral transmembrane proteins

• channel proteins

• carrier proteins

channel proteins

small and cylindrical in shape, the top, bottom and linear core are composed of hydrophillic Amino Acids attracting ions/polar molecules

• some are open all the time while others are gated, only opening when a signal is received like aquaporins with allow water to travel through the membranes

• muscle cells have gated ion channells which allow muscle contractions when opened

carrier proteins

are bigger and bulkier than channel proteins, and are only open on one side. The protein binds to that substance, changes the shape of it and carries it to the other side, the side that is open may change based on the concentration gradient

glucose transport protein

if we eat we will have a lot of glucose in our blood, the GLUTS move the glucose out of our bloodstream into our cells

osmosis

diffusion of water across a membrane

when does osmosis happen

when solute concentration is uneven and the solute can’t dissolve because it is to large and too charged

how does water move

it moves from an area of high H2O concentration to low H2O concentration, water is moving from area of low solute [] to high solute []

tonicity

how an extracellular solution can change the volume of a cell by affecting osmosis (how the solute [] outside of the cell affect the volume of fluid inside the cell by affecting osmosis)

osmolarity

describes the total solute [] of a solution

hypertonic extracellular solution

higher osmolarity outside the cell/solute concentration is higher outside the cell

hypotonic extracellular solution

higher osmolarity inside the cell/solute concentration is less outside the cell

isotonic extracellular solution

solute concentration/osmolarity is the same inside and out

what happens when a cell is in a hypotonic solution

water is going to move into the cell to dilute down that concentration, but ore water comes into the cell causing it so swell up/potentially burst (lysed

what happens when a cell is in a hypertonic solution

the concentration of solute is higher outside of the cell and water will move out of the cell causing it to shrivel up

what happens when the cell is in an isotonic solution

the concentrations inside and outside the cell are equal. This means equal amounts of H2O are moving in/out of the cell, Animal cells function best when extracellular fluids are isotonic

organisms with cell walls…

prefer hypotonic extracellular solutions, this happens because plant cells cant rupture because of the cell wall, the pressure against the cell wall (turgor pressure) is critical to organismal growth and function, a hypertonic solution causes plasmolysis (the plasma membrane detaches from the cell wall)

primary active transport

uses ATP; uses a membrane protein

secondary active transport

uses energy from a gradient (ATP used indirectly)/Always uses a membrane protein

uniporter pump

carry one type of molecule/ion either in or out of the cell

symporter pump

carries 2 different types of molecules or ions in the same direction either both into or out of the cell

antiporter pump

carries 2 different types of molecules or ions in different directions; one will be moving into the cell while the other is moving out

electrochemical (charge) gradients

when the solute that is imbalanced is an ion, When there is an imbalance of charge and solute concentration across the cell membrane.

what happens when ions move across